Attempts to characterize the neurotransmitter systems in man have focused on quantification of the neurotransmitter (serotonin 5HT), norepinephrine (NE), dopamine (DA), as well as various metabolites of these monoamines in various body fluids (urine, plasma, CSF). These neurotransmitter systems are suspected to be functioning abnormally in a variety of disorders (alcoholism, depression, schizophrenia, etc). In order to understand the meaning of measuring concentrations of neurotransmitters and their metabolites, it is necessary to understand their pharmacokinetics in the same and in different body compartments. Plasma and CSF concentrations, as well as 24 hour urinary measures of NE, DA and 5HT and their metabolites (VMA, MHPG, NM, 5HIAA, HVA) were collected in placebo treated, depressed subjects, alcoholics and healthy volunteers. Linear correlations were then calculated between these values within and between various body compartments. A better understanding of these relationships will help identify differences in formation, metabolism and elimination of these neurotransmitters in humans. This will offer insight into the functioning of these systems, and into the abnormalities of function that result in the previously observed abnormal concentrations of these neurotransmitters and their metabolites in certain disease states.